A generally employed method for producing a rail includes the processes of: heating a bloom and hot-rolling it into a predetermined shape; then cutting the hot-rolled material in lengths close to the final product lengths with a hot-sawing machine; thereafter applying or omitting a heat treatment depending on the required mechanical properties; cooling the cut materials to an ordinary temperature; applying or omitting a straightening treatment depending on the requirement; and subjecting the produced materials to predetermined inspections such as a flaw detection, a shape inspection and the like.
Rails are laid generally after connecting several rails with each other by welding in order to protect the ends of the rails from wear caused by the passages of trains. In such a case, as the wear increases when the welding planes deviate from each other even slightly, it is strictly required to minimize the deviation created when the end planes of rails are connected face to face. For example, JIS E1101 prescribes that the tolerance of a bend at an end of a 50 kgN rail, an ordinary rail, must be 1.0 mm or less in the rightward, leftward and upward directions and 0.3 mm or less in the downward direction, per 1.5 m in length. Further, a rail for a high-speed railway or a heavy-load railway, the demands for which have been increasing in recent years, is required to have a yet smaller bend at an end thereof. Furthermore, though the technologies of producing an ultra-long rail 500 feet or more in length at a stroke from a continuous casting process to a final process have been disclosed recently in U.S. Pat. Nos. 5,018,666 and 5,419,387, those technologies are seldom put to practical use in actual production.
However, when a rail is produced through a continuous process, an en of the rail is a portion to which rolling or straightening can hardly be applied. In a rolling process, it is difficult to achieve a required dimensional accuracy at a portion within the range from he tip or tail end of a rail to a position a certain length distant from either of them. In addition, when a straightening treatment is required and thus a straightener wherein a plurality of rolls are arranged in a zigzag pattern is used, the range from an end to a posit n about 1 to 2 m distant from the end, namely the range in the length corresponding to twice the interval between two adjacent rolls, is not leveled, namely becomes a dead zone, and therefore he effect of the straightening cannot be expected.
A practice commonly employed in order to satisfy the aforementioned criterion of a bend at an end of a rail in such a situation is to cut off a portion with a considerable length at an end of the rail and, when the criterion is not still satisfied even by doing so, to straighten the rail with a press. However, the longer the cut-off length, the higher the cost and the lower the yield. Further, as the cut-off process of a rail or the pressing process thereof requires time for the operation, each of the processes causes a bottleneck when it is incorporated into a continuous process. On the other hand, when each of the processes is employed as an off-line process, the productivity deteriorates. In particular, when a cold-sawing machine is employed and a cut-off is carried out at a high speed, a large amount of heat is generated, the heat affects only the cut-off end and, thus, the hardness or the like of the end changes largely, and it is therefore necessary either to regulate the cutting speed or to use a special device which does not generate a great amount of heat.
Furthermore, the problem here is that straightening by a press can hardly satisfy a precise dimensional accuracy and thus cannot cope with any future stringent criterion.